Pulse generation by changing magnetic field

ABSTRACT

A pulser unit is composed of two high strength magnets spaced apart from one another and establishing an intense magnetic field therebetween. Forward faces of the two magnets establish a working surface for the pulser unit. A Wiegand wire module consisting of a Wiegand wire segment around which a pickup coil is wound is mounted in the pulser unit immediately behind the working surface of the pulser unit and adjacent the sides of the two spaced apart magnets. The magnetic field is sufficiently strong to determine the state of the Wiegand wire. When a low reluctance element is brought adjacent to the front of the working surface, the field is substantially distorted and the field to which the Wiegand wire is subjected changes materially. The result is that the Wiegand wire switches state and the substantial rate of change of the flux in that switching of state is sensed by the pickup coil to provide an output pulse. Similarly, removal of the low reluctance element causes the field to revert so that the wire switches state back thereby inducing an output pulse in the pickup coil. The pulser can conveniently be kept stationary while the actuating low reluctance element is moved past the working face of the pulser.

BACKGROUND OF THE INVENTION

This invention relates in general to a mechanism for generating a pulseby switching the state of a magnetic device that has come to be known asa Wiegand wire and more particularly to a mechanism and method foraffecting the magnetic field to which a Wiegand wire module is subjectedso as to provide a reliable and repeatable output pulse upon theoccurrence of a predetermined event.

The magnetic device employed in the pulser of this invention is of thetype disclosed in U.S. Pat. No. 3,820,090 issued June 25, 1974. Apreferred embodiment of this magnetic device is disclosed in co-pendingapplication Ser. No. 897,483 filed Apr. 18, 1978, now U.S. Pat. No.4,247,601 and entitled "Switchable Magnetic Device and Method ofManufacturing Same". These magnetic devices are ferro-magnetic wiresegments which have been treated in such a fashion as to provide coreand shell portions with divergent properties and in particular divergentcoercivities. This type of wire has come to be known in the art asWiegand wire.

The Wiegand wire essentially has two states. In one of these states, themagnetization of the core and shell are in opposite directions and thisstate may conveniently be called a reverse state. In the other state,the magnetization of the core and shell are in the same direction andthis state may conveniently be called the confluent state. When themagnetic field to which the wire is subjected passes a threshold in onedirection or the other, the wire switches state. The switch in state isextremely rapid so that the rate of change of flux through a pickup coilwrapped around the wire is great. As a consequence the output from thepickup coil is very substantial, in some cases being as high as 8 voltsinto an open circuit on a repeatable basis. The wire and pickup coil isreferred to as a module.

Although certain techniques have been disclosed for switching the stateof the Wiegand wire, some of these techniques have not been appliedcommercially in a wide range of applications because of consideration ofcosts or size.

Accordingly, it is a major purpose of this invention to provide a highlyversatile pulser and pulsing arrangement employing a Wiegand wiremodule.

It is a related purpose to provide such a versatile item in a devicethat is simple and is relatively inexpensive to produce and to maintain.

It is another related purpose to provide the characteristics of low costand versatility while maintaining the reliability and repeatability ofresult that has been provided with previously known pulse generatingmechanisms employing the Wiegand wire.

Because the output pulse has to be taken off the pickup coil, it ispreferable that the module, consisting of Wiegand wire segment andpickup coil, be stationary in the pulse generator and that the movingelement be some ferro-magnetic element. Thus one purpose of theinvention is to provide a pulser design in which the output pulse can bedeveloped without moving the pulser unit.

BRIEF DESCRIPTION

In brief, in one embodiment of this invention, a stationary pulser unithas first and second spaced apart magnets which are aligned with oneanother so that their axes of magnetization are parallel to one anotherbut opposite in direction. These two magnets are small high strengthmagnets preferably made of a rare earth cobalt such as samarium cobalt.Thus, they establish a relatively intense field between them. TheWiegand wire module, which is essentially a Wiegand wire segment aroundwhich a pickup coil is wound, is positioned within the field between thetwo magnets. The outwardly facing north pole face of one of the twomagnets and the outwardly facing south pole face of the other of the twomagnets essentially define the plane of a working surface. The module isplaced in the field such that the axis of the wire segment is orthogonalto the axis of the magnets and is adjacent to and parallel to theworking surface of the magnets and also adjacent to and parallel to aside of each of the magnets.

When a low reluctance element is brought adjacent to and parallel tothis working surface, the configuration of the intense magnetic fieldbetween the two magnets changes substantially. This change in theconfiguration of the magnetic field substantially changes the magneticfield to which the Wiegand wire is subjected and by proper positioningof the wire in the magnetic field, this change of field switches thestate of the wire. When the low reluctance element is moved away, thefield reverts to its initial state thereby again changing the state ofthe wire. As the wire changes state, the pickup coil on the wireprovides an output pulse that can be used for any number of purposessuch as counting the number of times that the low reluctance element isbrought adjacent to the working surface of the pulser unit.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view of one embodiment of the invention in whichthe pulser element is pulsed by proximity to ferrous protrusions on theface of a rotating ferrous disk.

FIG. 2 is a second embodiment in which the pulser is actuated by ferrousprotrusions on the cylindrical surface of a rotating non-ferrous drum.

FIG. 2a is a cross-sectional view through the FIG. 2 embodimentillustrating the relative size and spacing involved.

FIG. 3 is a third embodiment of the invention illustrating anarrangement in which the pulser is pulsed by ferrous teeth attached tothe rim of a ferrous or nonferrous rotating disk.

FIG. 4 is a fourth embodiment in which the pulser is caused to pulse byproximity to gaps punched in a rotating ferrous disk.

FIG. 5 is a schematic illustration showing the relationship between themagnets of the Wiegand module within the pulser unit.

FIG. 6 is a schematic illustration similar to that of FIG. 5 except thatin FIG. 6 the field configuration is sketched in as it might appear whenone of the protrusions of FIGS. 1 or 2 are adjacent to the working faceof the pulser.

FIGS. 7 and 8 are schematic illustrations of the Wiegand effectexhibiting wire illustrating flux arrangement when in the confluentstate (FIG. 7) where core and shell magnetization are in the samedirection and when in the reverse state (FIG. 8) where core and shellmagnetization are in the opposite directions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 through 4 illustrate four pulse generator embodiments each ofwhich employ the same pulser unit 12. An electromagnetic schematic ofthe pulser unit 12 is shown in FIGS. 5 and 6.

VARIOUS PULSE GENERATOR EMBODIMENTS.

In FIG. 1 the working face of the pulser 12 is deployed adjacent to theface of a rotating disk 14. The disk 14 is a non-ferrous material on theface of which a plurality of ferrous modulators 16 are deployed asprotrusions. As the disk 14 rotates, the working face 12f of the pulser12 alternately is adjacent to a ferrous zone, defined by one of theprotrusions 16, and a non-ferrous zone, which is essentially the openspace between the protrusions 16. The existence of this ferrous (alsocalled ferro-magnetic) material 16 provides a low reluctance pathcausing the flux configuration generated by the magnets within thepulser 12 to materially distort and thereby change the magnetic fieldwhich influences the Wiegand wire. This is discussed in somewhat furtherdetail in connection with the discussion of FIGS. 5 and 6 below. Sufficeto say for now that the magnetized Wiegand wire in the pulser 12alternates between confluent state and reverse state as the alternateferrous protrusions and gaps are presented to the working face of thepulser 12. The resultant field change is picked up by a pickup coil as apulse on the output leads 17.

FIG. 2 illustrates another pulse generator embodiment in which arotating non-ferrous drum 18 has ferrous low reluctance elements 20deployed around the circumference of the drum. The ferrous elements 20determine a low reluctance zone and the space between the elements 20determine a high reluctance zone. The drum 18 is made of a non-ferrousmaterial. As shown in FIG. 2a, the gap between the pulser 12 and the lowreluctance elements 20 is kept small so that the effect of the elements20 on distorting or modifying the magnetic field is as substantial aspossible. In one embodiment, this gap between low reluctance element 20and the working face 12f is approximately 1.3 millimeters. This gap,although small, is sufficiently great so as not to require expensivedesign to maintain tight tolerances thereby keeping construction costsof the system reasonable for a wide variety of application.

FIG. 3 illustrates a third embodiment of the pulse generator in which aferrous or non-ferrous rotating disk 22 carries a series of ferrous lugs24 protruding from the rim of the disk. As each lug 24 passes theworking surface 12f of the pulser 12, a pulse output is produced at theleads 17.

FIG. 4 illustrates a fourth embodiment of the pulse generator structurein which a ferrous rotating disk 26 has a plurality of cut out orpunched out zones 28. As the open, high reluctance zones 28 alternatewith the low reluctance zones between the openings along the workingface 12f of the pulser 12, the state of the Wiegand wire in the pulser12 switches between its confluent and reverse states. Each switchproduces an output pulse on the output wires 17 from the pulser 12.

THE PULSER

The operation of the pulser 12 can better be understood by reference tothe electric and magnetic schematic illustrations in FIGS. 5 and 6. Twohigh energy magnets 30 and 32 are spaced from one another and inalignment such that their polar axes 30a, 32a are essentially paralleland such that a north pole face 30f of the first magnet and a south poleface 32f of the second magnet define the working surface 12f. In oneembodiment, samarium cobalt magnets 30, 32 are employed; each magnetbeing a bit over 6 millimeters long and being a bit over 3 millimeterson a side. They have a center-to-center spacing of approximately 13millimeters and thus establish a strong magnetic field between them.

A Wiegand wire module 33 comprising essentially a length of Wiegand wire34 around which a pickup coil 36 is wrapped is deployed in the magneticfield generated by the two magnets 30, 32. The module 33, in theillustrated embodiment, is deployed so that it is behind the workingsurface 12f and is adjacent to and substantially parallel to both theworking surface 12f and to the sides 30s, 32s of the magnets 30, 32. Thewire 34, positioned adjacent to one side of each of the two magnets, inone embodiment, has a length of approximately 20 millimeters therebyextending slightly past the outboard sides of the two magnets 30, 32.

The pickup coil 36 in that embodiment is wrapped around a 12 millimetercentral portion of the wire 34 and is constituted by 1,350 turns of No.44 wire. This embodiment produces an output pulse on the leads 17 thatis consistantly and reliably greater than one volt when applied to a2,000 ohm load, specifically the base of a transistor. Laboratorymeasurements show the open circuit output to be three and one-half tofour volts and thus consistantly meeting a specification requirement ofone volt. The Wiegand wire 34 is not in physical contact with the twomagnets but spaced from their sides by a small distance of 2.5millimeters.

The flux lines illustrated in FIGS. 5 and 6 are somewhat hypothesizedand have not yet been measured in detail. It should be understood thatthey are shown for illustrative purposes only. In FIG. 5, the flux linesare intended to represent the situation where a low reluctance elementis not present adjacent to the working surface 12f of the pulser 12. TheFIG. 5 drawing is intended primarily to illustrate this symmetry. When alow reluctance element, such as the element 20 of FIG. 2, is broughtadjacent to the working surface 12f, the flux pattern is substantiallychanged in a fashion approximately suggested by the schematic of FIG. 6.As shown in FIG. 6, the flux lines 40 in part are coupled through thelow reluctance element from one pole of each magnet to the other pole ofthe same magnet. When so coupled, the flux lines have a component thatis in the reverse direction from that of FIG. 5. Thus the field at thewire 34 is reversed sufficiently to force the wire 34 to change state.

RESUME OF THE FUNCTIONING OF THE WIRE

Although the Wiegand wire 34 has been described elsewhere, a briefdescription is provided here to facilitate understanding of thisdisclosure.

The wire 34 has two magnetic states as illustrated in FIGS. 7 and 8. Themanner in which the wire 34 is manufactured as well as a discussion ofthe nature of these two states may be found in the application Ser. No.897,483 referred to above supplemented by U.S. Pat. No. 3,820,090 issuedJune 25, 1974 to John R. Wiegand. The preferred form of the wire 34 foruse in this module 33 is disclosed in the patent application. The wire34 is a ferrous material such as the vanadium-cobalt-iron alloy or thenickle-iron alloy described in said patent application and patent. Thewire 34 typically has a diameter of 0.25 millimeters.

When the wire 34 is subjected to the field from the magnets 30, 32 (theFIG. 5 situation), it is magnetized and set into the state indicated inFIG. 7. In this state, the entire wire segment 34 is magnetized in asingle direction and this state is termed the confluent state. When thefield is distorted by the low reluctance element 20, then the wire 34will switch into its reverse state. In the reverse state, a relativelymagnetically hard shell portion 34s of the wire captures and reversesthe polarity of the relatively magnetically soft core portion 34c.Accordingly, the flux 40 generated by the relatively hard shell portion34s is coupled through the relatively soft core portion 34c and the fluxpattern changes from that shown in FIG. 7 to that shown in FIG. 8. Adiscussion of the magnetically hard shell portion 34s and themagnetically soft core portion 34c may be found in the referenced patentapplication and referenced patent.

When the low reluctance element 20 is removed, the field reverts tocause the wire 34 to switch back into its confluent state (the stateshown in FIG. 7). This change in the magnetic state of the wire causesthe flux generated by the shell portion 34s that was coupled through thecore 34c to complete its path outside of the wire 34.

In both cases where the wire switches state, the direction of flux 40through the core reverses and generates an electric pulse in the coil 36wrapped around the wire.

Although one embodiment of the pulser 12 has been described in somedetail and various pulse generator embodiments have been illustrated, itshould be understood that there are variations in the structureillustrated which are encompassed within the scope of the invention andit is intended that the appended claims cover these variations.

Some comment should be made with relation to the position of the module33. As shown in FIGS. 5 and 6, the module 33 is positioned adjacent tothe sides 30s, 32s of the two magnets. The module 33 is also positionedadjacent and rearward of the working surface 12f. In one example, theaxis of the wire 34 is 1.5 millimeters back from the working surface 12fand 2.5 millimeters from the magnet sides 30s, 32s. This positioning hasbeen found to provide effective and repeatable results and therefore ispresently a preferred position for the module 33. It has been found thatcertain other positions for the module are not as effective in producingusable results. For example, positioning the module 33 immediatelybehind the two magnets 30, 32 while maintaining the module orientationshown in FIGS. 5 and 6 appears to provide no usable output. It isbelieved that the reason for this is that the configuration of the fieldwhen it is distorted by the proximity of the low reluctance element,such as the element 20, is quite complex and that the wire segment 34must be positioned so that when the field has been distorted the fieldmust contain a component that sufficiently reverses the net externalfield on the wire 34 as to result in the desired switch of state for thewire. Accordingly, applicant would point out that changing the positionof the module within the pulser has to be tested on a case-by-case basisin order to determine if the desired state switch occurs.

What is claimed is:
 1. A pulser for use in the generation of a pulse inresponse to magnetic field distortion comprising:first and secondmagnets spaced apart from one another and oriented relative to oneanother so that a first pole of said first magnet and a second pole ofsaid second magnet define a working surface of said pulser, the polarityof said magnets having opposite orientation so that said first pole ofsaid first magnet and said second pole of said second magnet haveopposite polarities, said magnets establishing a magnetic field betweenthem, a Wiegand wire module having a predetermined position in the fieldbetween said magnets, said module including a Wiegand wire segment and apickup coil, said first and second magnets and said module all beingpositioned rearward of said working surface of the pulser, theconfiguration of said magnetic field between said magnets distortingmaterially in response to a material change in the reluctance pathprovided adjacent to and forward of said working surface of the pulser,said position of said Wiegand wire in said field being such that saidwire switches state in response to said material distortion of saidfield.
 2. The pulser of claim 1 wherein said module is positioned alonga plane adjacent a side of said magnets.
 3. The pulser of claims 1 or 2wherein said module is positioned along a plane adjacent said workingsurface.
 4. The pulser of claims 1 or 2 wherein said magnets are highenergy magnets. PG,13
 5. The pulser of claim 3 wherein said magnets aresamarium cobalt.
 6. The pulser of claim 4 wherein said magnets aresamarium cobalt.
 7. A pulse generator comprising:a pulser having aworking surface, and a low reluctance element, said pulser and saidelement being movable relative to each other such that said elementtraverses across said working surface of said pulser, adjacent to and infront of said working surface, said pulser including first and secondspaced apart magnets determining a magnetic field therebetween and aWiegand wire module positioned in said magnetic field between said firstand second magnets, said magnets and module all being positionedrearward of said working surface, said Wiegand wire module including aWiegand wire segment and a pickup coil wrapped around said segment, saidfirst and second magnets having essentially parallel magnetic axes andopposite polarities, a first pole of said first magnet having a firstpolarity and a second pole of said second magnet having a secondpolarity, said first pole of said first magnet and said second pole ofsaid second magnet substantially defining said working surface of saidpulser, the permeability of said low reluctance element being sufficientto materially distort said magnetic field between said magnets in thevicinity of said wire, when said element is adjacent said workingsurface, said wire switching state in response to said materialdistortion of said field.
 8. The pulser of claim 7 wherein said moduleis positioned along a plane adjacent a side of said magnets.
 9. Thepulser of claims 7 or 8 wherein said module is positioned along a planeadjacent said working surface.
 10. The pulser of claims 7 or 8 whereinsaid magnets are high energy magnets.
 11. The pulser of claim 9 whereinsaid magnets are samarium cobalt.
 12. The pulser of claim 10 whereinsaid magnets are samarium cobalt.
 13. The method of generating a pulsein response to the switching of state of a Wiegand wire wherein the wireis provided in a module having a pickup coil wrapped around a segment ofWiegand wire comprising the steps of:establishing a relatively intensemagnetic field between first and second magnets spaced from one anotherand polarized in opposite directions from one another, deploying theWiegand wire module in said field between said magnets and along a planeadjacent a side of said magnets, and bringing a low reluctance elementadjacent to a plane defined by a south pole of said first magnet and anorth pole of said second magnet to materially distort the configurationof the field in the vicinity of said module.